Encephalitis is inflammation, irritation, and swelling of the brain typically caused by a bacterial or viral infection. Less commonly, encephalitis can occur due to an overactive immune system that mistakenly attacks healthy brain cells. It’s a rare condition that usually affects young children, older adults, and immunocompromised people (e.g., those who live with HIV or are undergoing cancer treatment).

People who develop encephalitis may experience symptoms like fever, fatigue, and headaches. Symptoms start mildly but progress quickly, flaring up 1-2 weeks after the initial infection.

Encephalitis symptoms vary from person to person and will depend on the severity of inflammation in your brain. In severe cases, symptoms can progress enough to cause life-threatening complications, so seeking care for your symptoms is essential.

Because encephalitis results from an infection, its common symptoms are very similar to those of a flu or a cold. This makes the early diagnosis of encephalitis difficult, and sometimes cases can go undiagnosed. Several thousand cases are reported yearly, but research suggests that the number is higher due to undiagnosed cases.

The timeline for encephalitis symptoms varies. Mild cases are short and can last one or two weeks. The first two weeks of infection are the acute phase of the disease when symptoms are at their peak. Severe cases can last several months and may take even longer to recover from.

During the early stages of encephalitis, it’s common to experience the following symptoms:

As the infection progresses, symptoms can also fluctuate, meaning that you sometimes feel better while other symptoms worsen.

When you experience encephalitis, your brain and spinal cord become inflamed, which can cause several neurologic (brain-related) symptoms. This infection affects the normal function of your neurons (brain cells), causing symptoms such as:

• Memory difficulty
• Involuntary movements or seizures
• Clumsiness or difficulty with balance
• Difficulty speaking
• Impaired vision, double vision, or vision loss
• Body stiffness, rigidity, and tremors
• Loss of sensation in some parts of the body

Because of how encephalitis affects the brain, it’s not uncommon for people with the infection to experience changes in their psychological well-being. As a result, you may experience:

• Hallucinations
• Paranoia
• Sudden aggressive behavior
• Anxiety or panic attacks
• Difficulty sleeping
• Compulsive behaviors

Encephalitis can affect people assigned male or female at birth equally. Infections cause most cases of encephalitis. However, autoimmune encephalitis (which causes infection due to an overactive immune system) does have some differences based on sex, which affects which subtype of autoimmune encephalitis you might develop.

People assigned female at birth are more likely to be affected by NMDA receptor encephalitis. NMDA is a protein on the surface of neurons that controls communication between brain cells. Males are more likely to experience CASPR2 encephalitis. CASPR2 is a protein involved in communicating with brain cells and antibodies.

More research is being done to establish sex and gender differences in encephalitis development.

Encephalitis can affect children with a viral infection. A herpes infection usually causes cases of encephalitis in infants and newborns. It’s often harder to spot encephalitis symptoms in children because warning signs can look similar to other infections. These symptoms include:

• A bulge in the soft spot on the top of their head
• Severe and sudden vomiting
• Poor feeding
• Body stiffness
• Crying that gets worse when the child is picked up

If you suspect your child may be at risk for encephalitis, it’s important to seek care from their pediatrician immediately, as the infection can be more severe in young children.

While encephalitis is an infection, the condition itself is not contagious. However, the viral and bacterial infections (e.g., herpes, West Nile, etc.) that can cause encephalitis are contagious. These infections can spread through:

• Contact with an infected person’s saliva
• Breathing in droplets from a person with an infection
• Contaminated foods or drinks
• Kissing, sharing utensils, using the same toothbrush with a person who has an infection
• Parasites acquired via mosquitos, ticks, or other insects

Washing your hands regularly, cooking your meats all the way, drinking clean water, getting vaccinated, and avoiding contact with people with an active infection can help reduce your risk of developing an infection that can later cause encephalitis.

Encephalitis’s symptoms progress rapidly a week or two after the initial infection, and seeking care for this condition is essential, even if symptoms feel mild at first. Encephalitis can progress quickly and increase the risk of complications, so seeing a healthcare provider as soon as possible is important.

Some symptoms warrant more immediate medical attention. You should visit your healthcare provider immediately if you experience any of the following symptoms:

• Loss of consciousness
• Muscle weakness and paralysis
• Seizures
• Severe headaches
• Poor responsiveness
• A rapid change in your cognitive functions, including memory loss and impaired judgment

Encephalitis causes infection and inflammation in the brain, usually due to an underlying bacterial or viral infection. Common symptoms of this condition can include fatigue, fever, and headaches. However, encephalitis can also affect your brain functions and psychological well-being.

Encephalitis can often be hard to diagnose because symptoms in the early stages can mimic signs of other illnesses. However, if you have symptoms, even if they’re mild, contacting your healthcare provider is essential so you can reduce the risk of severe complications and receive proper treatment.